Various known bumper devices for vehicles are provided. For example, an attachment structure of a bumper reinforcement of a known bumper device is disclosed in JP2000-127873A (hereinafter referred to as Reference 1, see FIG. 1). In the bumper device according to Reference 1, the bumper reinforcement extends in a width direction of the vehicle. Crush boxes extending in a longitudinal direction of the vehicle are fixed to both end portions of the bumper reinforcement in the width direction by bolts and nuts. A clearance is formed between a rear wall portion of the bumper reinforcement and an inclined surface of each of the crush boxes. The inclined surface is inclined by a predetermined angle relative to the rear wall portion from an interior side in the width direction toward a rearward side of the vehicle. The crush box includes outer and inner panels in the width direction. For example, even in a case where a front collision of the vehicle occurs and the bumper reinforcement is thereby deformed, a compressive load acting in the longitudinal direction is inhibited by the aforementioned clearance from being applied to a front portion of a side surface of the inner panel.
Moreover, an attachment structure of a bumper reinforcement of a known bumper device for a vehicle is disclosed in JPH11 (1999)-208393A (hereinafter referred to as Reference 2, see FIG. 1). Side members extending in a longitudinal direction of the vehicle are arranged at both end portions of the bumper reinforcement extending in a width direction of the vehicle. Each of the end portions of the bumper reinforcement is fixed to a front end surface of each of the side members via a bumper stay by bolts and nuts. The bumper stay is formed by an extruded member, for example, made of aluminum alloy. The bumper stay includes a front wall portion, a longitudinal wall portion extending in the longitudinal direction, and a bead formed at the longitudinal wall portion. The front wall portion having a substantially triangle shape in cross section is formed to conform to an inclination of a curved shape of the end portion of the bumper reinforcement. The bead allows bending strength of the longitudinal wall portion to be lower than bending strength of the bumper reinforcement. Accordingly, for example, even in an occurrence of an offset collision against a portion of a front side of the vehicle, the side member is surely squashed in the longitudinal direction by the bead arranged at the longitudinal wall portion.
As described above, in the bumper device according to Reference 1, the crush box is fixed to the bumper reinforcement by the bolts and the nuts. Likewise, in the bumper device according to Reference 2, the bumper stay is fixed to the bumper reinforcement by the bolts and the nuts. Accordingly, the number of components of the bumper device according to each of References 1 and 2 increases. In addition, an axial length of each of the bolts and an axial length of each of the nuts are included in the longitudinal direction. Therefore, a length of the crush box or the bumper stay in the longitudinal direction needs to be increased in order to secure a compression distance in the longitudinal direction so that the crush box or the bumper stay may sufficiently absorb impact energy due to the aforementioned front collision or the offset collision. As a result, according to the bumper device disclosed in each of References 1 and 2, the length of each of the crush box and the bumper stay in the longitudinal direction needs to be increased.
A need thus exists for a bumper device for a vehicle, which is not susceptible to the drawback mentioned above.